1. Field of the Invention
This invention is directed to wellbore drilling top drive systems; bails to support parts thereof; and methods of their use.
2. Description of Related Art
The prior art discloses a variety of top drive systems; for example, and not by way of limitation, the following U.S. Patents present exemplary top drive systems and components thereof: U.S. Pat. No. 4,458,768; U.S. Pat. No. 4,807,890; U.S. Pat. No. 4,984,641; U.S. Pat. No. 5,433,279; U.S. Pat. No. 6,276,450; U.S. Pat. No. 4,813,493; U.S. Pat. No. 6,705,405; U.S. Pat. No. 4,800,968; U.S. Pat. No. 4,878,546; U.S. Pat. No. 4,872,577; U.S. Pat. No. 4,753,300; U.S. Pat. No. 6,007,105; U.S. Pat. No. 6,536,520; U.S. Pat. No. 6,679,333; U.S. Pat. No. 6,923,254—all these patents incorporated fully herein for all purposes.
Certain typical prior art top drive drilling systems have a derrick supporting a top drive which rotates tubulars, e.g., drill pipe. The top drive is supported by bails, often on a becket suspended beneath a travelling block beneath a crown block. A drawworks on a rig floor raises and lowers the top drive.
Certain prior art bails for supporting top drives have straight legs in which a three-cornered bail shape imparts stress-inducing bending moments throughout a bail when it is under load often with concentrated high stress locations at lower pin lugs and at a topmost upper bend. As larger and larger top systems have evolved, bails have simply been enlarged and made more massive to accommodate heavier system.